As an alternatives to cigarettes or as a way of quitting smoking, electronic cigarettes could simulate using effect of normal cigarettes and removes harmful composition such as tars, suspended particles in normal cigarettes, being sought after by people. At present, the electronic cigarettes in the market commonly adopt top oil-refilling structure. When refill with oil, the whole upper assembly or the heating assembly needs to be disassembled and the operation is complex, affecting user experience. There are other electronic cigarettes adopting bottom oil-refilling structure. However, several elements of electronic cigarette need to be disassembled. And it also has the disadvantages of oil-leakage and inconvenience of operation.